As a result of environmental and other concerns, plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities. As a result, blow-molded plastic containers have become commonplace in packaging numerous commodities.
Molds used to form such containers generally include four key features; A) a molding surface to form the container shape, B) vents formed in the cavity to atmosphere that allow air to egress the cavity as a preform inflates within the mold and ingress as the container exits the tool, C) a network of fluid channels routed within the cavity to achieve a desired mold temperature, and D) exterior mold mounting features matching machine hanger specifications.
Traditionally, one mold configuration for forming such containers includes a two-piece mold. A two-piece mold generally includes a mold holder and a cavity insert mounted within the mold holder. The cavity insert can define features A, B and C above, while feature D is defined in the hold holder. The mold holder and cavity insert are then fitted within a machine hanger. The machine hanger opens and closes the blow mold. Such two-piece mold configurations are typically used for containers having smaller diameters such as less than 95 mm (3.74 inches) for example, commonly referred to as 150 mm (5.91 inches) (referring to the inside diameter of the holder). For larger containers, a one-piece mold may be used. In a one-piece mold, all four of the above features, A, B, C and D are included in the cavity insert. Such one-piece mold configurations are used to accommodate formation of containers having diameters up to 140 mm (5.51 inches).
In either instance, it is necessary to cool the mold assembly during the mold process. In this way, cooling channels can be located within the cavity insert for delivering oil or other fluid through the cavity insert. As can be appreciated, designing and constructing such cavity inserts is complex and costly. Furthermore, because the cavity insert must be switched out when container designs change, each new mold cavity must be individually designed and formed with cooling channels routed through the structure. Thus, there is a need for a mold configuration that allows for simpler, more cost effective cooling of the mold cavity.